1. Field of the Invention
The present invention relates to a wireless communications system, and more particularly, to an event notification method in a wireless communications system which allows notification about an event, which is frequently generated, to be performed at specific time intervals by controlling time intervals of the event notification.
2. Description of the Background Art
SIP (Session Initiation Protocol) is a text-based protocol such as HTTP (Hypertext Transfer Protocol), in which one or more clients set up, modify and complete sessions. That is, the SIP is based on a client/server structure whereby if a client starts to make a call, a server responds to the calls. A voice communication service, an Instant Messaging service, a PoC (Push to talk of Cellular) service, or the like can be implemented by using an identifier having an address system similar to that used for an e-mail.
The SIP-based client subscribes with the server to be notified when a specific event is generated. The server sends an Event Notification to the corresponding SIP-based client when a specific event, to which the SIP-based client subscribes, is generated.
That is, the SIP-based clients subscribe with the server to a resource or call states for various resources, and notify the server when their own states are modified. In addition, the server sends an event notification to another SIP-based client which subscribe to be notified each time the states of the SIP-based clients are modified or each time the subscribed event is generated. Here, various SIP services can be implemented by using the event notification, such as a call-back service based on a terminal state event, a “buddy list” service based on a user presence event, a message wait indication service based on a mailbox state modification event, a PINT (PSTN/Internet Interworking) state service based on a call state event, or the like.
In an event notification method of the related art, since event notifications are sent to clients which subscribe to be notified whenever the subscribed event is generated, as corresponding events are generated more frequently or as more clients subscribe to the notification method with respect to the corresponding event, the server should transmit an increased amount of data as event notifications increase.
Hereafter, an exemplary procedure will be described with the assumption that a service is based on the user presence event.
The SIP-based client has a buddy list of other clients in order to use an instant messaging service or a PoC (Push-to-talk over Cellular) service. The buddy list is managed by a Presence Server. The presence server notifies a corresponding SIP client of presence information during a particular period of effective time after the SIP-based client subscribes to receive the presence information.
The SIP-based client notifies the presence server of any modified presence information if its own presence information is modified. The presence server sends an event notification in real-time to another client which subscribes to be notified of the modified presence information of the client. That is, as the number of buddies included in the buddy list increases, the amount of data transmitted over the wireless interface increases. Thus, transmission efficiency over the wireless interface is decreased.
As an another example of a related art method of notifying a corresponding event whenever a subscribed event is generated, there is provided a method of notifying a state regarding an event requested by the user at a specific point in time requested by the user.
In case of the service based on the user presence event, the user transmits a buddy list update request signal to the presence server at a specific point in time by using the SIP-based client, and the presence server receiving the buddy list update request signal transmits a response signal including presence information of the clients included in the corresponding buddy list to the SIP-based client.
However, the presence information update requested by the user is not an event notification method by which the user is automatically notified of a specific event on a subscription basis since the user should make a request at every point in time when the user checks specific information.
In addition, since the presence information of the buddy list is updated only when the user makes a request, the amount of data which should be transmitted at a time increases, a status of the buddy list cannot be checked in real-time, and thus the user is inconvenienced because his buddy list should be frequently checked.